共查询到20条相似文献,搜索用时 31 毫秒
1.
J. Reichert M. Sakaitani C. T. Walsh 《Protein science : a publication of the Protein Society》1992,1(4):549-556
EntF is the enzyme responsible for serine activation during the biosynthesis of enterobactin (a cyclic trimer of N-dihydroxybenzoyl serine) in Escherichia coli. EntF has been overexpressed and purified to > 90% homogeneity. The enzyme has been shown to complement the entF- MK1 strain in the synthesis of 2,3-dihydroxybenzoyl serine derivatives and exhibits L-serine-dependent ATP[32P] pyrophosphate exchange activity with a Km for serine of 260 mM and a turnover number of 760 min-1. Release of PPi during incubation of EntF with serine and ATP was observed, but with a low turnover number of 1.0 min-1. These results suggested the presence of an enzyme-bound intermediate, which has been shown by gel filtration analysis to be (L-serine)adenylate. 相似文献
2.
Enzymatic determination of itoic acid, a Bacillus subtilis siderophore, and 2,3-dihydroxybenzoic acid.
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
T Ito 《Applied microbiology》1993,59(7):2343-2345
A specific enzymatic method to determine the amounts of itoic acid, a Bacillus subtilis siderophore, and 2,3-dihydroxybenzoic acid (2,3-DHBA) was devised. A sample was incubated first with hippurate hydrolase and then with 2,3-DHBA-3,4-dioxygenase. Itoic acid was estimated from the increase in A374. The incubation with the first enzyme was omitted for the determination of 2,3-DHBA. 相似文献
3.
Kinetic evidence for the formation of D-alanyl phosphate in the mechanism of D-alanyl-D-alanine ligase 总被引:1,自引:0,他引:1
L S Mullins L E Zawadzke C T Walsh F M Raushel 《The Journal of biological chemistry》1990,265(16):8993-8998
The steady state kinetic mechanism, molecular isotope exchange and the positional isotope exchange (PIX) reactions of D-alanyl-D-alanine ligase from Salmonella typhimurium have been studied. The kinetic mechanism has been determined to be ordered Ter-Ter from initial velocity and product inhibition experiments. The first substrate to bind is ATP followed by the addition of 2 mol of D-alanine. Pi is released, and then D-alanyl-D-alanine and ADP dissociate from the enzyme surface. In the reverse direction D-alanyl-D-alanine exhibits complete substrate inhibition (Ki = 1.15 +/- 0.05 mM) by binding to the enzyme-ATP complex. In the presence of D-alanine, D-alanyl-D-alanine ligase catalyzed the positional exchange of the beta,gamma-bridge oxygen in [gamma-18O4]ATP to a beta-nonbridge position. Two possible alternate dead-end substrate analogs, D-2-chloropropionic acid and isobutyric acid, did not induce a positional isotope exchange in [gamma-18O4]ATP. The positional isotope exchange rate is diminished relative to the net substrate turnover as the concentration of D-alanine is increased. This is consistent with the ordered Ter-Ter mechanism as determined by the steady state kinetic experiments. The ratio of the positional isotope exchange rate relative to the net chemical turnover of substrate (Vex/Vchem) approaches a value of 1.4 as the concentration of D-alanine becomes very small. This ratio is 100 times larger than the ratio of the maximal reverse and forward chemical reaction velocities (V2/V1). This situation is only possible when the reaction mechanism proceeds in two distinct steps and the first step is much faster than the second step. The enzyme was also found to catalyze the molecular isotope exchange of radiolabeled D-alanine with D-alanyl-D-alanine in the presence of phosphate. These results are consistent with the formation of D-alanyl phosphate as a kinetically competent intermediate. 相似文献
4.
T Schwecke Y Aharonowitz H Palissa H von D?hren H Kleinkauf H van Liempt 《European journal of biochemistry》1992,205(2):687-694
delta-(L-alpha-Aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetase, the multienzyme catalyzing the formation of ACV from the constituent amino acids and ATP in the presence of Mg2+ and dithioerythritol, was purified about 2700-fold from Streptomyces clavuligerus. The molecular mass of the native enzyme as determined by gel filtration chromatography is 560 kDa, while that determined by denaturing gel electrophoresis is 500 kDa. The enzyme is able to catalyze pyrophosphate exchange in dependence on L-cysteine and L-valine, but no L-alpha-aminoadipic-acid-dependent ATP/PPi exchange could be detected. Other L-cysteine- and L-valine-activating enzymes present in crude extracts were identified as aminoacyl-tRNA synthetases which could be separated from ACV synthetase. The molecular mass of these enzymes is 140 kDa for L-valine ligase and 50 kDa for L-cysteine ligase. The dissociation constants have been estimated, assuming three independent activation sites, to be 1.25 mM and 1.5 mM for cysteine and ATP, and 2.4 mM and 0.25 mM for valine and ATP, respectively. The enzyme forms a thioester with alpha-aminoadipic acid and with valine in a molar ratio of 0.6:1 (amino acid/enzyme). Thus, the bacterial ACV synthetase is a multifunctional peptide synthetase, differing from fungal ACV synthetases in its mechanism of activation of the non-protein amino acid. 相似文献
5.
6.
Subcloning of the enterobactin biosynthetic gene entB: expression, purification, characterization, and substrate specificity of isochorismatase 总被引:1,自引:0,他引:1
The Escherichia coli entB gene, coding for the enterobactin biosynthetic enzyme isochorismatase, has been subcloned into the multicopy plasmid pKK223-3 under the control of the tac promoter. The resulting recombinant plasmid pFR1 expresses isochorismatase amounting to over 50% of the total cellular protein. The enzyme has been purified to homogeneity and a convenient assay developed. The enzyme has a Km for isochorismate of 14.7 microM and a turnover number of 600 min-1. By use of 1H NMR spectroscopy, the progress of the reaction was followed with the expected formation of 2,3-dihydro-2,3-dihydroxybenzoate product. Several substrate analogues were also utilized by the enzyme including chorismic acid, the immediate precursor to isochorismic acid in the enterobactin biosynthetic pathway. 相似文献
7.
2,3-Dihydroxybenzoic acid has been shown to be oxidized via the 3-oxoadipate pathway in the leaves of Tecoma stans. The formation of 2-carboxy-cis,cis-muconic acid, a muconolactone, 3-oxoadipic acid and carbon dioxide during its metabolism has been demonstrated using an extract of Tecoma leaves. The first reaction of the pathway, viz., the conversion of 2,3-dihydroxybenzoate to 2-carboxy-cis,cis-muconic acid has been shown to be catalysed by an enzyme designated as 2,3-dihydroxybenzoate 2,3-oxygenase. The enzyme has been partially purified and a few of its properties studied. The enzyme is very labile with a half-life of 3--4 h. It is maximally active with 2,3-dihydroxybenzoate as the substrate and does not exhibit any activity with catechol, 4-methyl catechol, 3,4-dihydroxybenzoic acid, etc. However, 2,3-dihydroxy-p-toluate and 2,3-dihydroxy-p-cumate are also oxidized by the enzyme by about 38% and 28% respectively, compared to 2,3-dihydroxybenzoate. Sulfhydryl reagents inhibit the enzyme reaction and the inhibition can be prevented by preincubation of the enzyme with the substrate. Substrate also affords protection to the enzyme against thermal inactivation. Sulfhydryl compounds strongly inhibit the reaction and the inhibition cannot be prevented by preincubation of the enzyme with its substrates. Data on the effect of metal ions as well as metal chelating agents suggest that copper is the metal cofactor of the enzyme. Evidence is presented which suggests that iron may not be participating in the overall catalytic mechanism. 相似文献
8.
2,3-Dihydroxybenzoate-2,3-oxygenase is mainly localized in the soluble and the chloroplast fractions of Tecoma leaves. It is associated with the lamellar structure of the chloroplast fraction. The chloroplast enzyme has properties similar to those of the soluble enzyme, but it has a longer half-life and is more stable to dialysis than the soluble enzyme. It is inhibited by sulfhydryl reagents and the inhibition is reversed by the addition of reduced glutathione. The chloroplast enzyme is insensitive to iron-chelating agents. The enzyme loses activity on dialysis against copper-chelating agents and the activity is completely recovered on the addition of copper; addition of iron does not restore the activity. Polyphenol oxidase is probably present only in the active form in the Tecoma chloroplast but it is not involved in the intradiol cleavage of 2,3-dihydroxybenzoic acid. 相似文献
9.
The substrate specificity of isoleucyl-tRNA synthetase from Escherichia coli MRE 600 with regard to ATP analogs has been compared with the results obtained with isoleucyl-tRNA synthetase from yeast. The enzyme from E. coli is less specific, the two enzymes exhibit different topographies of their active centres. The order of substrate addition to isoleucyl-tRNA synthetase from E. coli MRE 600 has been investigated by bisubstrate kinetics, product inhibition and inhibition by substrate analogs. The inhibition studies were done in the aminoacylation and in the pyrophosphate exchange reaction, the aminoacylation was investigated in the absence and presence of inorganic pyrophosphatase. As found for isoleucyl-tRNA synthetase from yeast, the results of the pyrophosphate exchange studies indicate the possibility of formation of E . Ile-AMP . ATP complexes by random addition of one ATP and one isoleucine molecule, followed by adenylate formation, release of pyrophosphate and subsequent addition of a second molecule of ATP. For the aminoacylation in the absence of pyrophosphatase, a rapid-equilibrium random ter addition of the substrates is found whereas the enzyme from yeast exhibits a steady-state ordered ter-ter mechanism; in the presence of pyrophosphatase the mechanism is bi-uni uni-bi ping-pong similarly as observed for the yeast enzyme. A comparison of inhibition patterns obtained with N(6)-benzyladenosine 5'-triphosphate under different assay conditions (spermine or magnesium ions, addition of pyrophosphatase) indicates that even more than two pathways of the aminoacylation may exist. The catalytic cycles of the two mechanisms derived from the observed orders of substrate addition and product release include the same enzyme substrate complex (E . tRNA . Ile-AMP) for the aminoacyl transfer reaction. The kcat values, however, are considerably different: kcat of the sequential pathway is about 40% lower than kcat of the ping-pong mechanism. 相似文献
10.
Isopentenyl pyrophosphate isomerase catalyzes the interconversion of isopentenyl pyrophosphate and dimethylallyl pyrophosphate. The isomerase from yeast has been purified to near homogeneity (purity greater than 90%). The substrate analogue (Z)-3-(trifluoromethyl)-2-butenyl pyrophosphate reacts at less than 1.8 X 10(-6) times the rate of dimethylallyl pyrophosphate. The enzyme is irreversibly inactivated by 2-(dimethyl-amino)ethyl pyrophosphate (I). These observations are consistent with a carbonium ion mechanism for the isomerization. Compound I is an analogue of the intermediate carbonium ion and probably acts as a transition state analogue. For I, kon' = 2.1 X 10(6) M-1 min-1. No off-rate was detected and, therefore, Ki less than 1.4 X 10(-11) M. Upon denaturation of the inactivated enzyme, I is released unchanged. 2-(Trimethylammonio)ethyl pyrophosphate also inhibits with Ki' = 7 X 10(-7) M, kon' = 4.4 X 10(4) M-1 min-1, and koff = 0.03 min-1. Substrate analogues without a positively charged nitrogen were relatively poor inhibitors. The best inhibitor of these is ethyl pyrophosphate, Ki = 10(-4) M. The enzyme is inactivated by sulfhydryl-selective reagents. These reagents also prevent binding of I to the enzyme. The inactivation by iodoacetamide is dependent upon one ionizable group (pK = 9.3). The pH dependence of V and V/K for the isomerase-catalyzed reaction also depends upon a group with pK = 9.3. 相似文献
11.
Pantothenate synthetase from Mycobacterium tuberculosis catalyzes the formation of pantothenate from ATP, D-pantoate, and beta-alanine. The formation of a kinetically competent pantoyl-adenylate intermediate was established by the observation of a positional isotope exchange (PIX) reaction within (18)O-labeled ATP in the presence of d-pantoate. When [betagamma-(18)O(6)]-ATP was incubated with pantothenate synthetase in the presence of d-pantoate, an (18)O label gradually appeared in the alphabeta-bridge position from both the beta- and the gamma-nonbridge positions. The rates of these two PIX reactions were followed by (31)P NMR spectroscopy and found to be identical. These results are consistent with the formation of enzyme-bound pantoyl-adenylate and pyrophosphate upon the mixing of ATP, D-pantoate, and enzyme. In addition, these results require the complete torsional scrambling of the two phosphoryl groups of the labeled pyrophosphate product. The rate of the PIX reaction increased as the D-pantoate concentration was elevated and then decreased to zero at saturating levels of D-pantoate. These inhibition results support the ordered binding of ATP and D-pantoate to the enzyme active site. The PIX reaction was abolished with the addition of pyrophosphatase; thus, PP(i) must be free to dissociate from the active site upon formation of the pantoyl-adenylate intermediate. The PIX reaction rate diminished when the concentrations of ATP and D-pantoate were held constant and the concentration of the third substrate, beta-alanine, was increased. This observation is consistent with a kinetic mechanism that requires the binding of beta-alanine after the release of pyrophosphate from the active site of pantothenate synthetase. Positional isotope exchange reactions have therefore demonstrated that pantothenate synthetase catalyzes the formation of a pantoyl-adenylate intermediate upon the ordered addition of ATP and pantoate. 相似文献
12.
The release of iron from transferrin was investigated by incubating the diferric protein in the presence of potential iron-releasing agents. The effective chemical group appears to be pyrophosphate, which is present in blood cells as nucleoside di- and triphosphates, notably adenosine triphosphate (ATP). An alternative structure with comparable activity is represented by 2,3-diphosphoglycerate. Neither 1 mM adenosine monophosphate (AMP) nor 1 mM orthophosphate released iron from transferrin. The ATP-induced iron-releasing activity was dependent on weak acidic conditions and was sensitive to temperature and sodium chloride concentration. The rate of iron release rapidly increased as transferrin was titrated with HCl from pH 6.8 to 6.1 in the presence of 1 mM ATP and 160 mM NaCl at 20 degrees C. Iron release from transferrin without ATP was observed below pH 5.5. Ascorbate (10(-4) M) reduced Fe(III), but only after iron release from transferrin by a physiological concentration of ATP. A proposal for the mechanism of iron release from transferrin by ATP and the utilization of reduced iron by erythroid cells is described. 相似文献
13.
The enzymatic conversion of 3'-phosphate terminated RNA chains to 2',3'-cyclic phosphate derivatives 总被引:1,自引:0,他引:1
The enzyme, RNA cyclase, has been purified from cell-free extracts of HeLa cells approximately 6000-fold. The enzyme catalyzes the conversion of 3'-phosphate ends of RNA chains to the 2',3'-cyclic phosphate derivative in the presence of ATP or adenosine 5'-(gamma-thio)triphosphate (ATP gamma S) and Mg2+. The formation of 1 mol of 2',3'-cyclic phosphate ends is associated with the disappearance of 1 mol of 3'-phosphate termini and the hydrolysis of 1 mol of ATP gamma S to AMP and thiopyrophosphate. No other nucleotides could substitute for ATP or ATP gamma S in the reaction. The reaction catalyzed by RNA cyclase was not reversible and exchange reactions between [32P]pyrophosphate and ATP were not detected. However, an enzyme-AMP intermediate could be identified that was hydrolyzed by the addition of inorganic pyrophosphate or 3'-phosphate terminated RNA chains but not by 3'-OH terminated chains or inorganic phosphate. 3'-[32P](Up)10Gp* could be converted to a form that yielded, (Formula: see text) after degradation with nuclease P1, by the addition of wheat germ RNA ligase, 5'-hydroxylpolynucleotide kinase, RNA cyclase, and ATP. This indicates that the RNA cyclase had catalyzed the formation of the 2',3'-cyclic phosphate derivative, the kinase had phosphorylated the 5'-hydroxyl end of the RNA, and the wheat germ RNA ligase had catalyzed the formation of a 3',5'-phosphodiester linkage concomitant with the conversion of the 2',3'-cyclic end to a 2'-phosphate terminated residue. 相似文献
14.
Catabolism of tryptophan, anthranilate, and 2,3-dihydroxybenzoate in Trichosporon cutaneum. 总被引:6,自引:6,他引:0
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Trichosporon cutaneum degraded L-tryptophan by a reaction sequence that included L-kynurenine, anthranilate, 2,3-dihydroxybenzoate, catechol, and beta-ketoadipate as catabolites. All of the enzymes of the sequence were induced by both L-tryptophan and salicylate, and those for oxidizing kynurenine and its catabolites were induced by anthranilate but not by benzoate; induction was not coordinate. Molecular weights of 66,100 and 36,500 were determined, respectively, for purified 2,3-dihydroxybenzoate decarboxylase and its single subunit. Substrates for this enzyme were restricted to benzoic acids substituted with hydroxyl groups at C-2 and C-3; no added coenzyme was required for activity. Partially purified anthranilate hydroxylase (deaminating) catalyzed the incorporation of one atom of 18O, derived from either 18O2 or H2(18)O, into 2,3-dihydroxybenzoic acid. 相似文献
15.
Studies on the activating enzyme for iron protein of nitrogenase from Rhodospirillum rubrum 总被引:7,自引:0,他引:7
L L Saari M R Pope S A Murrell P W Ludden 《The Journal of biological chemistry》1986,261(11):4973-4977
Removal of ADP-ribose from the iron protein of nitrogenase by activating enzyme resulted in the activation of the inactive iron protein. A radioassay that directly measured the initial velocity of the activation was developed using iron protein radiolabeled with either [8-3H]- or [G-32P]ADP-ribose. The release of radiolabeled ADP-ribose by activating enzyme was linearly correlated with the increase in the specific activity of the iron protein as measured by acetylene reduction. Both ATP and MnCl2 were required for the activation of inactive iron protein. The optimal ratio of [MnCl2]/[ATP] in the radioassay was 2:1, and the optimal concentrations were 4 mM and 2 mM for [MnCl2] and [ATP], respectively. The Km for inactive iron protein was 74 microM and the Vmax was 628 pmol of [32P] ADP-ribose released min-1 microgram of activating enzyme-1. Adenosine, cytidine, guanosine, or uridine mono-, di-, or triphosphates did not substitute for ATP in the activation of native iron protein. Activating enzyme removed ADP-ribose from oxygen-denatured iron protein in the absence of ATP. ADP, ADP-ribose, pyrophosphate, and high concentrations of NaCl inhibited activating enzyme activity. 相似文献
16.
Over-production, purification and properties of the uridine diphosphate N-acetylmuramoyl-L-alanine:D-glutamate ligase from Escherichia coli. 总被引:3,自引:0,他引:3
F Pratviel-Sosa D Mengin-Lecreulx J van Heijenoort 《European journal of biochemistry》1991,202(3):1169-1176
The UDP-N-acetylmuramoyl-L-alanine:D-glutamate ligase of Escherichia coli was over-produced in strains that harbour recombinant plasmids bearing the murD gene under the control of the lac or PR promoter. Purification to homogeneity was achieved by a two-step procedure from a 181-fold over-producing strain. The N-terminal sequence of the purified protein was determined and correlated with the nucleotide sequence of the murD gene. The purified activity was highly dependent on the concentration of potassium phosphate and Mg2+. The enzyme also catalysed the reverse reaction. The Km values for UDP-N-acetylmuramoyl-L-alanine; D-glutamate and ATP/Mg2+ were estimated at 7.5, 55 and 138 microM, respectively. Under the most optimal in vitro conditions determined, a turnover number of 931 min-1 was estimated. When considering the plasmid-free parental strain, the copy number of the murD gene product was not more than 1000.cell-1. 相似文献
17.
A new pathway for the aerobic metabolism of 2-aminobenzoate which proceeds via 2-aminobenzoyl-CoA has recently been revealed in a Pseudomonas strain KB 740-. The enzyme catalyzing the first step, the formation of the coenzyme A (CoA) thioester of 2-aminobenzoate, is 2-aminobenzoate-CoA ligase. It was purified from cells aerobically grown with 2-aminobenzoate as sole carbon, energy, and nitrogen source and characterized. It is rather specific for 2-aminobenzoate, but activates also benzoate and fluorobenzoates. ATP was cleaved into AMP and pyrophosphate. The ligase is a monomer of M(r) 65,000, as determined by gel filtration and SDS/PAGE. The N-terminal amino acid sequence was determined and the gene locus of the enzyme was identified by Southern blot hybridization on a small 8-kbp plasmid pKB 740. The 1.8-kb nucleotide sequence of the 2-aminobenzoate-CoA ligase gene and the derived amino acid sequence of the native enzyme (597 residues) are reported. 相似文献
18.
Vaccinia virus gene SalF 15R potentially encodes a polypeptide of 63 kD which shares 30% amino acid identity with S. pombe and S. cerevisiae DNA ligases. DNA ligase proteins can be identified by incubation with alpha-(32P)ATP, resulting in the formation of a covalent DNA ligase-AMP adduct, an intermediate in the enzyme reaction. A novel radio-labelled polypeptide of approximately 61 kD appears in extracts from vaccinia virus infected cells after incubation with alpha-(32P)ATP. This protein is present throughout infection and is a DNA ligase as the radioactivity is discharged in the presence of either DNA substrate or pyrophosphate. DNA ligase assays show an increase in enzyme activity in cell extracts after vaccinia virus infection. A rabbit antiserum, raised against a bacterial fusion protein of beta-galactosidase and a portion of SalF 15R, immune-precipitates polypeptides of 61 and 54 kD from extracts of vaccinia virus-infected cells. This antiserum also immune-precipitates the novel DNA ligase-AMP adduct, thus proving that the observed DNA ligase is encoded by SalF 15R. 相似文献
19.
目的:苯甲酸脱羧酶能够催化羧化反应固定CO2,为了获得高效的苯甲酸脱羧酶,需要利用高通量分子克隆与突变体筛选系统对产生的大量突变体进行筛选,因此建立、开发高效的筛选评价方法对于获得高羧化效率的突变体至关重要。方法:利用2,3-二羟基苯甲酸脱羧酶催化邻苯二酚固定CO2的反应体系,建立了光谱法-图像灰度法高通量筛选和评价固定CO2的苯甲酸脱羧酶突变体。利用分光光度法在308 nm快速定量羧化产物2,3-二羟基苯甲酸。同时利用高效液相色谱(HPLC)法对分光光度法的测定结果进行了校正,确定了分光光度法估算的2,3-二羟基苯甲酸浓度与HPLC方法测定的准确浓度之间具有良好的线性关系(R2 = 0.996)。利用HPLC-分光光度法的相关性可以获得实际样品中准确的2,3-二羟基苯甲酸浓度。利用Image J软件获得蛋白质标准品和突变体的灰度均值,根据灰度法定量蛋白质标准品的标准曲线计算突变体的蛋白质表达量。利用单位酶量催化邻苯二酚获得2,3-二羟基苯甲酸的浓度比较突变体的催化活性。结果:纯酶和粗酶体系下HPLC法测定的2,3-二羟基苯甲酸浓度与分光光度法测定的吸光度值的关系分别为C1=0.500A1-0.010(R2 = 0.996)和C2=1.458A2+0.431 9(R2 = 0.991)。从13个突变体中获得了两个正向突变体,羧化活性分别是WT的3.5倍和1.7倍。结论:基于光谱法-图像灰度法可以实现高通量筛选固定CO2的苯甲酸脱羧酶,该方法可用于具有相似功能的苯甲酸脱羧酶对其他取代基的酚类和水杨酸类似物的底物选择性筛选。 相似文献
20.
During the purification of L-tryptophan 2,3-dioxygenase, a protohemoprotein from rat liver, both copper and heme contents of the preparations were found to be progressively increased as purification proceeded. However, the greater part of copper was removed in the late stages of the purification giving a copper to heme ratio less than 0.4. The small amounts of copper could further be reduced by one-half, by a mild treatment of enzyme with chelators such as ethylenedi aminetetraacetate, without any accompanying decrease in enzymatic activity. Since the turnover number of these enzyme preparations expressed per mol of enzyme-bound heme, 200 to 277 min-1 at 25 degrees, were either comparable to or slightly higher than those reported with homogeneous enzyme preparations, the heme in the preparation was considered to be of fully active L-tryptophan 2,3-dioxygenase and, therefore, such a small ratio of copper to heme, 0.1 to 0.3, indicated that copper is not a constituent of L-tryptophan 2,3-dioxygenase of rat liver. The findings were thus inconsistent with the results of Brady et al. (Brady, F. O., Monaco, M. E. Forman, H. J. Schutz, G., and Feigelson, P. (1972) J. Biol. Chem. 247, 7915-7922), who found that L-tryptophan 2,3-dioxygenase contained 2 g atoms of copper and 2 mol of heme/mol of enzyme. Possible reasons for this discrepancy have been discussed. 相似文献